The purpose of the experiments contained in the present research proposal is to examine empirically the impact of normal aging and abnormal aging (the impact of Alzheimer's disease) on perceptual matching, spatial recognition memory, and visual search tasks. The participants will be healthy young and older adults, and older adults with Alzheimer's disease (AD). The goals of the current project are to: (a) test the viability of an internal noise model of cognitive aging, (b) distinguish differences in cognitive functioning related to normal aging from those associated with AD. Experiments 1-3 will examine the performances of healthy young and older adults on perceptual matching tasks (Experiment 1 will also test AD patients). The relative speed and accuracy with which subjects respond to "same" and "different" trials will be used to test the validity of the internal noise model. Experiments 4-6 will examine age differences on a spatial, recognition memory task for order information (Experiment 4 will also test AD patients). The internal noise model of cognitive aging predicts that transposition distance should impact upon reaction time (RT) and/or accuracy. Specifically, Correct rejection RTs and/or false alarm errors should increase as transposition distance decreases, and this effect should be larger for older adults. Experiments 7 and 9 will use more "ecologically valid" task to examine age differences in spatial recognition memory. A "clock face" task will be used where the minute and/or hour hand(s) of a clock face will be shifted relative to where they originally appeared on part of the trials (Experiment 7 will also test AD patients). Experiment 8 will test healthy older adults and AD patients on three paper-and-pencil tasks in order to examine the impact of linguistic deficits, perseveration, and context on AD patients' typically poor performance on production tasks for spatial memory. Using a visual search task, Experiments 10-12 will vary the number of instances of a target letter (i.e., redundancy) on a given trial. Also, half the trials will involve perceptual noise. The internal noise model predicts that older adults should exhibit relatively larger redundancy effects for noise trials than for no-noise trials on this visual search task where redundancy is varied from one to three instances. If the current tasks can separate healthy older adults from AD patients (i.e., Experiments 1, 4, 7-8, and 10), then these tasks could be used as assessment tools for indexing AD.